The job sla and metadata, which are part of the job header sent to the driver and then to the nodes, are never used anywhere once the job has been executed. Removing them from the results sent by the node to the driver, the driver to antoher driver and the driver to a client will decrease both network traffic and serialization/deserialization time, without affecting anything else.

Thus we propose to set them to null before sending results back to a remote peer.

Really delete this comment?

This is now implemented. I could measure a slight performance improvement (about 3%) with the basic 300x300 matrix multiplication sample.
The effect will be most sensitive with jobs that have a small number of short-lived tasks.